1. Field of the Invention
The present invention relates to a temperature detection circuit for use in an overheat protection circuit or the like.
2. Description of the Related Art
FIG. 6 is a circuit diagram for illustrating a configuration example of a related-art temperature detection circuit.
A constant current circuit 108, a diode 102, and a variable resistor 113 are connected in series between a power supply terminal 10 and a ground terminal 11. The diode 102 has an anode connected to the constant current circuit 108 and a gate of a P-channel transistor 111, and a cathode connected to the variable resistor 113. A resistor 109 and a resistor 110 are connected in series between the power supply terminal 10 and the ground terminal 11. A node between the resistor 109 and the resistor 110 is connected to a gate of an N-channel transistor 112. The P-channel transistor 111 has a source connected to the power supply terminal 10 and a drain connected to an output terminal 12. The N-channel transistor 112 has a drain connected to the output terminal 12 and a source connected to the ground terminal 11.
When temperature increases, a voltage generated across the diode 102 decreases, and the absolute value of a threshold voltage (Vth) of the P-channel transistor 111 decreases.
Accordingly, when temperature increases, the threshold voltage (Vth) of the P-channel transistor 111 and a voltage between the power supply terminal 10 and the gate terminal of the P-channel transistor 111 are reversed in magnitude, and then the P-channel transistor 111 is turned on. Thus, a voltage of the output terminal 12 is inverted from a voltage of the ground terminal 11 to a voltage of the power supply terminal 10.
A resistance value of the variable resistor 113 is set to an appropriate value in order to adjust a detection temperature of the temperature detection circuit.
In the related-art temperature detection circuit, however, in order to adjust the detection temperature, the resistance value of the variable resistor 113 needs to be adjusted in consideration of the threshold voltage of the P-channel transistor 111 and its temperature characteristics, a current value of the constant current 108 and its temperature characteristics, and temperature characteristics of the variable resistor 113.